Seizure Imaging: Surgery for Medically Intractable Epilepsy Unni Udayasankar MD Assistant Professor Cleveland Clinic Children’s Hospital Objectives • Common indications and rationale for pediatric epilepsy surgery • Review the role of imaging in preoperative assessment • Understand the major types of epilepsy surgery performed • Radiopathological correlation in surgical causes of epilepsy Identifying Surgical Candidates • Medical intractability in Epilepsy: – Two appropriately chosen, well-tolerated first line antiepileptic drug regimens have failed due to lack of efficacy. – Where the minimum seizure free period is one year or 3 times the pretreatment inter-seizure interval, whichever is longer. • Surgical candidacy to be determined on a case by case basis using data from an extensive multimodality assessment. • Plasticity phenomenon: Early surgical intervention can maximize efficacy, recovery, and cognitive potential. *Kwan P, Arzimanoglou A, Berg ST, et al. Definition of drug resistant epilepsy. Consensus proposal by the ad hoc Task Force of the ILAE Commission on Theraputic Strategies. Epilepsia. 2010; 51:1069-77. Key Considerations for Surgery Is a structural lesion identified? (MRI) Is an epileptogenic zone identified? (EEG, functional imaging) Are the lesion and epileptogenic zone concordant? Location? Relationship to eloquent cortex? (MR landmarks, functional imaging) Focal or extensive? Single or multiple? Unilateral or bilateral? Presurgical Assessment Modalities EEG MRI PET/SPECT fMRI Subdural grid MEG DTI/Tractography Invasive electrodes fMRI Motor Passive Listening Rhyming Word generation Nuclear Medicine Studies • Interictal Positron Emission Tomography (PET) • Ictal Single Photon Emission Computed Tomography (SPECT) • Identify eloquent cortex to be spared • Identify or confirm ictal focus • Identify pathophysiology of partial and generalized seizures • ictal hypermetabollism will be seen not only in the source lesion, but in any cortex to which the seizure has spread Common Types of Epilepsy Surgery Goals of surgery: – To resect the epileptogenic zone, OR – To disconnect avenues of seizure spread Types of surgery – Lesionectomy – Temporal Lobectomy – Hemispherectomy – Corpus Callosotomy – Multiple Subpial Transections – Radiosurgery – Vagal nerve stimulators Lesionectomy Focal Cortical Dysplasia • Most common cause • Types – FCD Type I (non-Taylor) A and B – FCD Type II (Taylor) • Two variants – Hemimegalencephaly – Tuberous sclerosis FCD FCD Taylor Type IIB with balloon cells FCD: Lesionectomy FCD: Taylor Type II Multifocal lesionectomy Tuberous sclerosis MCD Lesionectomy: Tumors • Almost all originate from cerebral cortex • Mixture of glial and neural elements • Benign biological behavior • Low mitotic activity • Stable or slow growing • Associated with cortical dysplasia or dysplastic neuronal elements Ganglioglioma PXA PXA DNET Oligodendroglioma Pilomyxoid Astrocytoma (PMA) Angiocentric glioma Atypical Meningioma Lesionectomy: Cavernous malformation Lesionectomy: Scar Lesionectomy: Post herpetic encephalomalacia Temporal Lobectomy • Intractable temporal lobe lesion – Malformations of cortical development – Neoplasm – Mesial Temporal Sclerosis (MTS) – Vascular anomalies Temporal Lobectomy Selective Amygdalohippocampectomy “Standard” Anterior Temporal Lobectomy Temporal Lobectomy Temporal Lobectomy Selective Amygdalohippocampectomy In selective amygdalohippocampectomy, goal is to preserve remaining temporal lobe. Access to mesial structures is challenging; approaches include trans-Sylvian, lateral trans-cortical, subtemporal, and variations. Temporal Lobectomy: MCD Temporal Lobectomy: Ganglioglioma Temporal Lobectomy: Oligodendroglioma Cavernous Malformation Right temporal AVM Extended Lesionectomy/Lobectomy Aicardi syndrome Cystic Encephalomalacia Sturge Weber Syndrome Sturge Weber Syndrome Sturge-Weber Syndrome Grade II Oligoastrocytoma Polymicrogyria Schizencephaly Old non-accidental injury Hemispherectomy • Typical Indications: Secondary generalized seizures where focus is large or multifocal involving only one hemisphere. – Rasmussens Encephalitis – Ishemic or traumatic injury – Sturge Weber – Hemimegencephly – Diffuse (unilateral) migration disorder • Two main techniques share goal of rendering disordered hemisphere behaviorly non-functional. 1. Anatomic Hemispherectomy – Remove involved hemisphere, leaving only deep structures. 2. Functional Hemispherectomy – Disconnect white matter tracts with more limited resection. Anatomic Hemispherectomy • When anatomic hemispherectomy is considered, the epileptogenic hemisphere is usually severely dysfunctional – Hemiparesis – Language mediated by the contralateral hemisphere • Therefore extensive resection may be justified. • Frontal, parietal, occipital and temporal lobes are removed, leaving the basal ganglia, thalamus, and brainstem. Anatomic Hemispherectomy: Large MCD Hemimegalencephaly Hemimegalencephaly Anatomic Hemispherectomy: Chronic Post surgical changes Functional Hemispherectomy • A “window” of cortex may be removed to then make the appropriate white matter transections. • White matter tracts that are disconnected – Corpus Callosum – Coronal radiata/internal capsule – Fornix – Anterior Commisure – Outflow tracts of the amygdala Functional Hemispherectomy Rassmussen’s encephalitis Rassmussen’s Encephalitis Cystic encephalomalacia , functional hemispherectomy Functional Hemispherectomy . Corpus Callosotomy • Typical Indications: – Intractable seizures without resectable focus or when only incomplete resection is possible – Patients may have multiple epileptogenic zones – Drop attacks Corpus Callosotomy Multiple Subpial Transections • Typical Indications: Epileptogenic zone in dominant eloquent cortex • A “disconnection” type procedure to avoid resecting eloquent structures: Hypothalamic Hamartoma Epilepsy Surgeries Summary Surgical Objectives Technique Candidates Example lesions •Neoplasm Discrete resectable •Vascular Lesionectomy lesions (usually non- •Focal MOCD eloquent cortex) Resection: •Encephalomalacia Remove the Temporal Lesions isolated to •Any of above involving temporal epileptogenic focus Lobectomy temporal lobe lobe, including MTS Anatomic Hemispher- •Sturge-Weber Extensive or multifocal ectomy •Rasmussen’s unilateral epileptogenic Encephalitis Functional foci Hemispher- •Hemimegancephaly ectomy Disconnection: Extensive or multifocal •Extensive MOCD Interrupt cortical Corpus bilateral epileptogenic •Lesion of dominant connections to limit foci or no resectable Callosotomy eloquent cortex seizure spread focus Multiple Subpial Epileptogenic foci in •Lesion of dominant Transections eloquent cortex eloquent cortex .